Indium tin oxide (ITO) is widely used as the conductor in the transparent electrodes that are essential to the functioning of many different types of display devices. ITO has a number of drawbacks. These include brittleness, which can lead to handling difficulties on flexible substrates, and a high refractive index that can give rise to reflective losses in constructions utilizing ITO layers on polymer films. The latter is a particular problem for liquid crystal-based devices, in that reflective losses at the electrode/active layer interface can lead to decreases in transmission, in turn leading to lower contrast ratios and degradation of display performance. Furthermore, ITO films are generally deposited using vacuum processing, which can be problematical if expensive vacuum deposition equipment is not readily available. They also depend on the availability of indium metal, an expensive, limited, and potentially strategic resource. Thus, many flexible display devices could benefit from availability of alternative transparent conducting electrodes which are not based on ITO and can be prepared by roll-to-roll wet coating processing.
Silver has the highest bulk conductivity of any known material. Consequently, one class of coatings exhibiting great promise as a roll-coatable ITO replacement is silver nanowires. These materials can be coated from liquid dispersions using standard roll-to-roll coating methods such as slot die and gravure. Although such coatings can give excellent conductivity with high visible transmission and low haze, in some applications the oxidative and chemical instability of silver, particularly in nanowire form, can necessitate the use of a protective overcoat for the silver layer to protect it against mechanical, chemical, and environmental degradation and subsequent loss of conductivity properties.